1. Field of the Invention
The present invention relates to the production of thin wall castings of metals, such as aluminum and alloys thereof, by casting processes such as sand casting followed by heat treatment and quenching to retain the necessary distortion, hardness and tensile properties. In known metal casting processes, a mold is provided and molten metal is poured thereinto to fill the mold cavity. After cooling, the mold is opened or broken away and the metal casting is removed, heat-treated to develop the necessary high strength properties, and quenched.
The casting of thin wall metallic elements, such as flat plates and similar articles, has been limited to the casting of minimum wall thicknesses of about 0.120 inch. Wall thicknesses below this minimum result in castings which warp or "oil can" during quenching and otherwise lack dimensional stability, strength and stiffness so as to be difficult to handle, non-uniform in dimensions and appearance, and deflective under load.
The necessity for thicker wall metal castings increases the weight and the cost of the castings, and requires the additional steps of chemical milling and/or machining in cases where some of the weight must be removed. Such steps involve additional time and expense and can result in the disadvantages discussed above if substantial amounts of wall metal are removed.
Thin wall metallic elements having stiffness and resistance to warping are conventionally produced by the weld assembly of several machined or formed parts. However such elements are either rolled from thin sheet material and formed, or are machined from thick plate and assembled, and therefore are more expensive.